This invention relates to metallurgy sphere, particularly to the methods of alloy melting, making use of high-alloyed waste as pieces and fine-dispersed particles containing large amount of non-metal component.
There is a well-known and widely used method by which the waste of ALNIKO alloy, including powder-like one of grinding process, that contains large quantity of a non-metal component is melted and oxidizing refined in an open furnace and then the melt is poured. After this the alloy obtained is melted in another installation followed by additional alloying up to definite composition. (Aba K. Kinzoku: 1977, v.47, No. 10, p.26-30). The main disadvantage of above method is the considerable loss of waste fine-dispersed component because. some amount of it turns as suspended matter to ambient of furnace open space in melting. This powder is irretrievably taken away by effluent gases. Another disadvantage of that method is the restriction related to the possibility of using the powder-like waste in charge (no more than 50%). These restrictions are caused by the difficulty of powder-like waste melting with electric arc.
An object of this invention is to increase the waste metal component and the percentage of possible using of the powder-like charge component through the maintaining the melting conditions at which the waste is remelted in liquid flux the base of present invention makes. With this the harmful non-metal component is bound with flux and the powder-like waste could be remelted practically unlimitedly.
To this aim the method of ALNIKO alloy melting, is proposed, including the charge melting followed by its oxidizing refining. In accordance with the invention the proposed method supposes the charge melting in the layer of flux heated by electric current passed through it. The metal component of powder-like waste is absorbed by flux and the suspended matter irretrievably taken away from the furnace atmosphere by effluent gases does not form. As a result the waste utilization coefficient increases. The liquid flux favors the melting of powder-like part of waste allowing to increase its percentage in charge.
Undesirable impurities (carbon, silicon, chromium etc.) are moved away when using the solid oxidizers (scale, ore etc.) and the gaseous oxygen in melting at the expense of oxidizing refining. With this the aluminium as the most easy oxidized element is also moved away. The quantity of the aluminium remainder in melt is an indication of oxidizing refining efficiency.
If starting charge is very soiled and full extraction of undesirable impurities is riot possible at this stage of melting then the melt is transferred into another installation xe2x80x94a mixer or an induction furnace xe2x80x94wherein the final oxidizing refining is carried out. Then the metal is additionally alloyed up to predetermined chemical composition in the same installation.
When the necessary melt purity is succeeded to attain at first stage of process then the melt is transferred into a mixer or into an induction furnace in order to average its chemical composition and there only additional alloying up to ALNIKO alloy composition is carried out.
The quantity of a non-metal component in the waste used for melting could not be less than 3% because this is the minimal level of soiling at which the oxidizing refining is necessary at all. On the other hand the quantity of a non-metal component should not be more than 60% because otherwise the electrical regime of melting is disturbed.
The oxidizing refining of melt up to remainder aluminium concentration not less than 0.05% is supposed in charge melting in the layer of liquid flux. At these concentrations of aluminium the degree of melt oxidation is sufficient for removing off all undesirable impurities to definite limits. If the content of remainder aluminium in melt is less than 0.05% then the melt will be superoxidized resulting in loss of the components when alloying. At the same time the amount of the remainder aluminium at this stage of melt refining should not be more than 1% because it would be difficult to carry out final refining in induction furnace due to fast growing over of crucible walls with aluminium oxides.
The melting has to be carried out at temperatures more not less than 1500 xc2x0 C. because otherwise the metal will not be melted. At the same time the temperature should not be higher than 1800xc2x0 C. because of intensive corrosion of crucible magnesite lining by melt.